Method for forming hole pattern

ABSTRACT

A photosensitive material film is formed by applying, on an etch target film deposited on a semiconductor substrate, a photosensitive material containing a hardly alkaline-soluble base polymer including a polymer in which a principal chain has cycloolefin and a saturated or non-saturated polycyclic alkyl group is bonded to the principal chain, and an acid generator including an onium salt compound. The photosensitive material film is irradiated with ArF excimer laser through a photomask so as to form a hole-patterned photosensitive material film. A hole pattern is formed in said etch target film by subjecting the etch target film to plasma etching using plasma at a plasma density of 1×10 10 /cm 3  or more with the hole-patterned photosensitive material film used as an etching mask.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for forming a holepattern. More particularly, it relates to a method for forming a finehole pattern of an etch target film formed on a semiconductor substratethrough dry etching of the etch target film by using an etching mask ofa hole-patterned photosensitive material film with ArF excimer laserused as exposing light.

[0002] As a conventional example, a method for forming a hole patterndisclosed in Japanese Laid-Open Patent Publication No. 2000-66384 willnow be described with reference to FIGS. 5A through 5C. FIG. 5B is across-sectional view taken along line VB-VB of FIG. 5A.

[0003] In this conventional method, a chemically amplified resistmaterial having the following constituents is used:

[0004] Base polymer: a polymer in which an adamantyl group is bonded asa protecting group to an acrylic copolymer

[0005] Acid generator: onium salt

[0006] Solvent: propylene glycol monomethyl ether acetate

[0007] First, as shown in FIGS. 5A and 5B, the chemically amplifiedresist material having the aforementioned constituents are applied on anetch target film 2 formed on a semiconductor substrate 1, and theresultant is annealed at 90 for 90 seconds, thereby forming aphotosensitive material film 3 with a thickness of 700 nm.

[0008] Next, the photosensitive material film 3 is irradiated with KrFexcimer laser through a photomask having a transmission portion with adiameter of, for example, 300 nm, and then, annealing is carried out asPEB (post-exposure baking) at 110 for 90 seconds. Thereafter, thephotosensitive material film 3 is developed. Thus, the photosensitivematerial film 3 is formed into a hole pattern having a hole 3 a with adiameter of, for example, 300 nm.

[0009] Then, as shown in FIG. 5C, the etch target film 2 is subjected toplasma etching by using the hole-patterned photosensitive material film3 as an etching mask. Thus, a hole 2 a for a contact hole or a via holeis formed in the etch target film 2.

[0010] Recently, there are increasing demands for a higher degree ofintegration and further refinement of semiconductor integrated circuitdevices. Accordingly, the shape of the hole 2 a formed in the etchtarget film 2 is required to be more vertical (so as to attain an angleof the side wall of 75 through 90 degrees) and the aspect ratio (thedepth of the hole/the diameter of the hole) is required to be increased.For example, when the aspect ratio of the hole 2 a is approximately 1through 2, a substantially vertical shape (with the angle of the sidewall of 75 through 90 degrees) is required and the hole 3 a is requiredto be formed to attain a high aspect ratio of approximately 2 or more.

[0011] Furthermore, as shown in FIGS. 6A and 6B, there arises a problemthat the hole 2 a formed in the etch target film 2 has not only astar-like plane shape but also a diameter (hole size) much larger thanthe desired value (300 nm).

[0012] According to Japanese Laid-Open Patent Publication No.2000-66384, in order to form the hole 2 a with a high aspect ratio inthe etch target film 2, plasma with a plasma density of 1×10¹⁰/cm³ ormore, which is higher than a conventionally employed density, is used inthe plasma etching so as to form the hole 2 a of the etch target film 2in a circular plane shape. Furthermore, the acid generator including anonium salt compound is used so as to prevent the hole size from becomingmuch larger than the desired value.

[0013] In the lithography process for forming the hole-patternedphotosensitive material film, KrF excimer laser (of a wavelength of 248nm) is conventionally used as the exposing light. Recently, however, inorder to cope with the higher degree of integration and furtherrefinement of semiconductor integrated circuits, ArF excimer laser (of awavelength of 193 nm) is proposed to be used as the exposing light. Whenthe ArF excimer laser is used, the hole size can be reduced toapproximately 200 nm.

[0014] However, when the photosensitive material film formed from theaforementioned chemically amplified resist material is irradiated withthe ArF excimer laser for forming the hole pattern, although the oniumsalt compound is used as the acid generator, the hole of the etch targetfilm is formed in a star-like plane shape and the hole size is muchlarger than the desired value (200 nm).

[0015]FIG. 7 shows the relationship between the plasma density and theplane shape and the hole size of a hole formed through the lithographyprocess using ArF excimer laser as the exposing light. The relationshipof FIG. 7 is obtained in the case where an etch target film of BPSG(boro-phospho silicate glass) with a thickness of 1200 nm formed on asilicon substrate is subjected to plasma etching by using ahole-patterned photosensitive material film with a thickness of 700 nm,and the hole size is set to 200 nm.

[0016] In this case, in a low plasma density region corresponding to anRIE region where the plasma density is lower than 1×10¹⁰/cm³, the holeformed in the etch target film has a circular plane shape and the holesize is 200 nm, which is substantially equal to that of thehole-patterned photosensitive material film. In contrast, in a highplasma density region where the plasma density is 1×10¹⁰/cm³ or more,the hole formed in the etch target film has a star-like plane shape andthe hole size is enlarged.

[0017] Accordingly, it is understood that although the acid generatorincluding the onium salt compound is used, when the plasma density is1×10¹⁰/cm³ or more, the plane shape of the hole formed in the etchtarget film is changed from a circular shape to a star-like shape andthe hole size is abruptly enlarged.

[0018] When the hole has a star-like plane shape or the hole size ismuch larger than a desired value, a metal film filled in the hole isconnected to an interconnect that should not be electrically connectedto the metal film. As a result, there arises a problem that an abnormalleakage current flows or that the device characteristic is degraded.

[0019]FIGS. 8A and 8B show the relationship between the reduction of thehole size and the problem of the star-like plane shape of the hole orthe enlargement of the hole size. FIG. 8A shows a hole with a hole sizeof 0.20 {grave over (l)}m and FIG. 8B shows a hole with a hole size of0.30 {grave over (l)}m. In either case, the hole size is enlarged byapproximately 0.5 {grave over (l)}m.

[0020] In the hole of FIG. 8B, the enlargement rate of the hole size is1.17 (0.35/0.30), and in the hole of FIG. 8A, the enlargement rate ofthe hole size is 1.25 (0.25/0.20). In other words, even when the holesize is enlarged by the same dimension, the enlargement rate isincreased as the hole size is reduced, which largely affects the planeshape of the hole to change it to a star-like shape.

SUMMARY OF THE INVENTION

[0021] In consideration of the aforementioned conventional problems, anobject of the invention is, in forming a fine hole pattern with a highaspect ratio by irradiating a photosensitive material film made from achemically amplified resist material with ArF excimer laser, forming ahole in a circular plane shape in an etch target film and preventing thehole from having a diameter much larger than a desired value (200 nm).

[0022] In order to achieve the object, the present inventors havevariously examined the cause of the star-like plane shape of a holeformed in an etch target film, resulting in finding the following: Inthe case where an acrylic copolymer is used as a base polymer, althoughthe base polymer is good for attaining high sensitivity and highresolution, when a hole pattern of the etch target film is formed byplasma etching at a plasma density of 1×10¹⁰/cm³ or more, the wall ofthe hole is easily scraped.

[0023] This is because the photosensitive material film is exposed tothe high density plasma, so that a straight-chain bond is broken in theacrylic copolymer, which makes the etching resistance of thephotosensitive material film uneven. The etching resistance of thephotosensitive material film at issue corresponds to the specialty of apattern of the hole pattern, and means, in an actual device, that theremaining rate of the photosensitive material film is very high in ahole pattern as compared with that in a line pattern. Therefore, in thecase where the etch target film is subjected to the plasma etching,stress can be easily collected in a hole pattern than in a line pattern,and hence, the shape of a hole pattern is more easily changed.

[0024] The etching resistance at issue corresponds to the change to thestar-like shape caused because of the distribution in the etch rate ofthe photosensitive material film. It does not correspond to improvementof etch selectivity between the photosensitive material film and theetch target film (namely, prevention of the photosensitive material filmfrom being etched while etching the etch target film) as described in,for example, paragraph [0070] of Japanese Laid-Open Patent PublicationNo. 10-254140.

[0025] In the case where polyhydroxystyrene, which is widely used as abase polymer of a chemically amplified resist material in using KrFexcimer laser as the exposing light, is used in the exposure of ArFexcimer laser, a pattern is difficult to form because the lighttransmittance is low.

[0026] The present invention was devised on the basis of theaforementioned findings, and specifically, the first method for forminga hole pattern of this invention comprises the steps of forming aphotosensitive material film by applying, on an etch target filmdeposited on a semiconductor substrate, a photosensitive materialcontaining a hardly alkaline-soluble base polymer including a polymer inwhich a principal chain has cycloolefin and a saturated or non-saturatedpolycyclic alkyl group is bonded to the principal chain, and an acidgenerator including an onium salt compound; forming a hole-patternedphotosensitive material film by irradiating the photosensitive materialfilm with ArF excimer laser through a photomask; and forming a holepattern in the etch target film by subjecting the etch target film toplasma etching using plasma at a plasma density of 1×10¹⁰/cm³ or morewith the hole-patterned photosensitive material film used as an etchingmask.

[0027] The second method for forming a hole pattern of this inventioncomprises the steps of forming a photosensitive material film byapplying, on an etch target film deposited on a semiconductor substrate,a photosensitive material containing a hardly alkaline-soluble basepolymer including a polymer in which a principal chain is composed ofcyclo with three or more folds ring, and an acid generator including anonium salt; forming a hole-patterned photosensitive material film byirradiating the photosensitive material film with ArF excimer laserthrough a photomask; and forming a hole pattern in the etch target filmby subjecting the etch target film to plasma etching using plasma at aplasma density of 1×10¹⁰/cm³ or more with the hole-patternedphotosensitive material film used as an etching mask.

[0028] According to the first or second method for forming a holepattern of this invention, since the base polymer has high stabilityagainst heat and plasma, the wall of the hole formed in thephotosensitive material film is difficult to scrape even when plasmaetching is carried out by using plasma at a high density of 1×10¹⁰/cm³or more. Accordingly, a hole having a high aspect ratio and a good planeshape with a hole size not largely enlarged as compared with a desiredvalue can be formed in the etch target film. Also, since the acidgenerator includes an onium salt compound, the resistance of thephotosensitive material film against the plasma etching can be furtherimproved.

[0029] As a result, a metal film filled in the hole of the etch targetfilm is not connected to an interconnect that should not be electricallyconnected to the metal film, and hence, the problem of an abnormalleakage current or degradation of the device characteristic can beprevented.

[0030] In the first method for forming a hole pattern, the polymerpreferably includes a norbornene derivative.

[0031] Alternatively, in the first method for forming a hole pattern,the polymer preferably includes norbornene and a norbornene derivative.

[0032] In the first method for forming a hole pattern, the polycyclicalkyl group is preferably an adamantyl group, a tricyclodecyl group or atetracyclododecyl group.

[0033] In the second method for forming a hole pattern, the polymerpreferably includes a tricyclodecene derivative, a tetracyclododecenederivative, a pentacyclopentadecene derivative or a hexacycloheptadecenederivative.

[0034] In the second method for forming a hole pattern, a saturated ornon-saturated polycyclic alkyl group is preferably bonded to theprincipal chain of the polymer.

[0035] In the first or second method for forming a hole pattern, theplasma etching is preferably carried out by using a first voltage forgenerating plasma and a second voltage for inducing ions of the plasmatoward the semiconductor substrate.

[0036] Thus, the plasma etching can be definitely carried out by usingplasma at a high density of 1×10¹⁰/cm³ or more.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIGS. 1A, 1B and 1C are diagrams for showing procedures in amethod for forming a hole pattern according to Embodiment 1 or 2 of theinvention, and specifically, FIG. 1A is a plane view, FIG. 1B is across-sectional view taken along line IB-IB of FIG. 1A and FIG. 1C is across-sectional view;

[0038]FIGS. 2A and 2B are diagrams for showing another procedure in themethod for forming a hole pattern of Embodiment 1 or 2, andspecifically, FIG. 2A is a plane view and FIG. 2B is a cross-sectionalview taken along line IIB-IIB of FIG. 2A;

[0039]FIGS. 3A, 3B and 3C are diagrams for showing procedures in amethod for forming a hole pattern according to Embodiment 3 of theinvention, and specifically, FIG. 3A is a plane view, FIG. 3B is across-sectional view taken along line IIIB-IIIB of FIG. 3A and FIG. 3Cis a cross-sectional view;

[0040]FIGS. 4A, 4B and 4C are diagrams for showing other procedures inthe method for forming a hole pattern of Embodiment 3, and specifically,FIG. 4A is a cross-sectional view, FIG. 4B is a plane view and FIG. 4Cis a cross-sectional view taken along line IVC-IVC of FIG. 4B;

[0041]FIGS. 5A, 5B and 5C are diagrams for showing procedures in aconventional method for forming a hole pattern, and specifically, FIG.5A is a plane view, FIG. 5B is a cross-sectional view taken along lineVB-VB of FIG. 5A and FIG. 5C is a cross-sectional view;

[0042]FIGS. 6A and 6B are diagrams for explaining problems of theconventional method for forming a hole pattern, and specifically, FIG.6A is a plane view and FIG. 6B is a cross-sectional view taken alongline VIB-VIB of FIG. 6A;

[0043]FIG. 7 is a characteristic diagram for showing the relationshipbetween plasma density and the plane shape and hole size of a holeformed through a lithography process using ArF excimer laser as exposinglight; and

[0044]FIGS. 8A and 8B are diagrams for explaining the relationshipbetween reduction of a hole size and a problem of a star-like planeshape of a hole or enlargement of a hole size.

DETAILED DESCRIPTION OF THE INVENTION

[0045] EMBODIMENT 1

[0046] A method for forming a hole pattern according to Embodiment 1 ofthe invention will now be described with reference to FIGS. 1A through1C, 2A and 2B.

[0047] In Embodiment 1, a chemically amplified resist material havingthe following constituents is used:

[0048] Base polymer: a hardly alkaline-soluble polymer in which anadamantyl group is bonded as a protecting group to a copolymer of anorbornene derivative and maleic anhydride

[0049] Acid generator: triphenylsulfonium triflate, that is, an oniumsalt compound

[0050] Solvent: a mixed solvent of propylene glycol monomethyl etheracetate and ethyl lactate

[0051] First, as shown in FIGS. 1A and 1B, the chemically amplifiedresist material having the aforementioned constituents is applied on anetch target film 11 deposited on a semiconductor substrate 10, and then,annealing is carried out at 90 for 90 seconds, thereby forming aphotosensitive material film 12 with a thickness of 700 nm.Subsequently, the photosensitive material film 12 is irradiated with ArFexcimer laser through a photomask having a transmission portion with adiameter of, for example, 200 nm, and then, annealing is carried out asPEB at 110 for 90 seconds.

[0052] Next, an irradiated portion (exposed portion) of thephotosensitive material 12 is dissolved in a developer of a 2.38% TMAHaqueous solution. Thus, the photosensitive material film 12 is formedinto a hole pattern made from an unirradiated portion (unexposedportion) of the photosensitive material film and having a hole 12 a witha hole size of 200 nm.

[0053] The chemically amplified resist material has transmittance of 55%or more against the ArF excimer laser, and hence, the hole 12 a with ahole size of 200 nm can be formed.

[0054] When the photosensitive material film is patterned by using KrFexcimer laser as the exposing light instead of the ArF excimer laserwith the other conditions of the method of Embodiment 1 unchanged, ahole with a hole size of 200 nm cannot be formed.

[0055] However, since the aforementioned chemically amplified resistmaterial is used in Embodiment 1, the hole-patterned photosensitivematerial film 12 having a hole size of 200 nm can be formed through thepattern exposure using the ArF excimer laser as the exposing light.

[0056] Next, as shown in FIG. 1C, the etch target film 11 is subjectedto plasma etching with the hole-patterned photosensitive material film12 used as an etching mask under the following conditions:

[0057] Plasma etching system: induction coupling plasma (ICP) system

[0058] Etching gas: a C₂F₆ gas

[0059] Degree of vacuum in chamber: 665 through 1330 kPa

[0060] Bias power: 1000 W

[0061] Source power: 2100 W

[0062] The plasma density is thus set to 1×10¹⁰/cm³ through 1×10¹²/cm³.In this manner, a hole 11 a is formed in the etch target film 11.

[0063] When the hole 11 a is formed in the etch target film 11 under theabove-described conditions, the hole 11 a with a circular plane shapeand a hole size of approximately 205 nm can be formed without largelyenlarging the hole size as compared with the desired value as shown inFIGS. 2A and 2B.

[0064] Furthermore, according to Embodiment 1, when the hole 11 a has anaspect ratio of approximately 1 through 2, it is formed in asubstantially vertical shape (with an angle of the side wall of 75through 90 degrees). Moreover, when the hole 11 a has a high aspectratio of 2 through 8, it is formed in a shape with the side wall taperedtoward the bottom, namely, with the cross-sectional dimension reducedtoward the bottom.

[0065] Although an adamantyl group is used as the protecting group inthis embodiment, a non-substituted polycyclic alkyl group such as atricyclodecyl group and a tetracyclododecyl group may be used instead.Alternatively, a substituted polycyclic alkyl group in which a hydroxylgroup or an alkoxy group is substituted for such a group may be usedinstead.

[0066] Although the copolymer of a norbornene derivative and maleicanhydride is used as the base polymer in this embodiment, a norbornenederivative, a copolymer of norbornene and a norbornene derivative or acopolymer of norbornene, a norbornene derivative and maleic anhydridemay be used instead.

[0067] EMBODIMENT 2

[0068] A method for forming a hole pattern according to Embodiment 2 ofthe invention will now be described with reference to FIGS. 1A through1C, 2A and 2B.

[0069] In Embodiment 2, a chemically amplified resist material havingthe following constituents is used:

[0070] Base polymer: a hardly alkaline-soluble polymer in which anadamantyl group is bonded as a protecting group to a copolymer of atricyclodecene derivative and maleic anhydride

[0071] Acid generator: triphenylsulfonium triflate, that is, an oniumsalt compound

[0072] Solvent: a mixed solvent of propylene glycol monomethyl etheracetate and ethyl lactate

[0073] First, as shown in FIGS. 1A and 1B, the chemically amplifiedresist material having the aforementioned constituents is applied on anetch target film 11 deposited on a semiconductor substrate 10, and then,annealing is carried out at 90 for 90 seconds, thereby forming aphotosensitive material film 12 with a thickness of 700 nm.Subsequently, the photosensitive material film 12 is irradiated with ArFexcimer laser through a photomask having a transmission portion with adiameter of, for example, 200 nm, and then, annealing is carried out asthe PEB at 110 for 90 seconds.

[0074] Next, an irradiated portion (exposed portion) of thephotosensitive material 12 is dissolved in a developer of a 2.38% TMAHaqueous solution. Thus, the photosensitive material film 12 is formedinto a hole pattern made from an unirradiated portion (unexposedportion) of the photosensitive material film and having a hole 12 a witha hole size of 200 nm.

[0075] The chemically amplified resist material has transmittance of 55%or more against the ArF excimer laser, and hence, the hole 12 a with ahole size of 200 nm can be formed.

[0076] When the photosensitive material film is patterned by using KrFexcimer laser as the exposing light instead of the ArF excimer laserwith the other conditions of the method of Embodiment 2 unchanged, ahole with a hole size of 200 nm cannot be formed.

[0077] However, since the aforementioned chemically amplified resistmaterial is used in Embodiment 2, the hole-patterned photosensitivematerial film 12 having a hole size of 200 nm can be formed through thepattern exposure using the ArF excimer laser as the exposing light.

[0078] Next, as shown in FIG. 1C, the etch target film 11 is subjectedto plasma etching with the hole-patterned photosensitive material film12 used as an etching mask under the following conditions:

[0079] Plasma etching system: induction coupling plasma (ICP) system

[0080] Etching gas: a C₂F₆ gas

[0081] Degree of vacuum in chamber: 665 through 1330 kPa

[0082] Bias power: 1000 W

[0083] Source power: 2100 W

[0084] The plasma density is thus set to 1×10¹⁰/cm³ through 1×10¹²/cm³.In this manner, a hole 11 a is formed in the etch target film 11.

[0085] When the hole 11 a is formed in the etch target film 11 under theabove-described conditions, the hole 11 a with a circular plane shapeand a hole size of approximately 203.5 nm can be formed as shown inFIGS. 2A and 2B, and thus the enlargement of the hole size is suppressedas compared with that in Embodiment 1.

[0086] This is because a tricyclodecene derivative is included in thebase polymer, namely, the base polymer has a triple cyclo-ringdifferently from the norbornene derivative used in Embodiment 1, andhence, the etching resistance is improved. Accordingly, the enlargementof the hole size can be further suppressed in Embodiment 2 than inEmbodiment 1.

[0087] Furthermore, according to Embodiment 2, when the hole 11 a has anaspect ratio of approximately 1 through 2, it is formed in asubstantially vertical shape (with an angle of the side wall of 75through 90 degrees). Moreover, when the hole 11 a has a high aspectratio of 2 through 8, it is formed in a shape with the side wall taperedtoward the bottom, namely, with the cross-sectional dimension reducedtoward the bottom.

[0088] Although a tricyclodecene derivative, that is, a polymer having atriple cyclo-ring, is used in this embodiment, a tetracyclododecenederivative having a four-fold cyclo-ring, a pentacyclopentadecenederivative having a five-fold cyclo-ring or a hexacyclopentadecenederivative having a six-fold cyclo-ring may be used instead. When apolymer having a cyclo-ring of four or more folds is thus used, theresistance against etching in high density plasma can be furtherimproved. Therefore, the enlargement of the hole size can be furthersuppressed so as to form a hole in a better shape.

[0089] Although an adamantyl group is used as the protecting group inthis embodiment, a non-substituted polycyclic alkyl group such as atricyclodecyl group and a tetracyclododecyl group may be used instead.Alternatively, a substituted polycyclic alkyl group in which a hydroxylgroup or an alkoxy group is substituted for such a group may be usedinstead.

[0090] Thus, the resistance against etching in high density plasma canbe further improved, and hence, the enlargement of the hole size can befurther suppressed so as to form a hole in a better shape.

[0091] Furthermore, since the polymer composed of cyclo with three ormore folds ring is used as the base polymer in this embodiment, when anacetal group, a tert-butoxycarbonyloxy group or the like is used as theprotecting group instead of a polycyclic alkyl group, the enlargement ofthe hole size can be suppressed so as to form a hole in a good shape.

[0092] Although the copolymer of a tricyclodecene derivative and maleicanhydride is used as the base polymer in this embodiment, atetracyclododecene derivative, a copolymer of tetracyclododecene and atetracyclododecene derivative, a copolymer of tetracyclododecene, atetracyclododecene derivative and maleic anhydride, a copolymer ofnorbornene and a tetracyclododecene derivative or a copolymer ofnorbornene, a tetracyclododecene derivative and maleic anhydride may beused instead.

[0093] Although an onium salt compound is singly used as the acidgenerator in Embodiment 1 or 2, a mixture of an onium salt compound withanother acid generator such as a sulfonimide compound, ahalogen-containing compound, a sulfone compound and a sulfonic estercompound may be used instead.

[0094] An acid generator of a sulfonimide compound, a halogen-containingcompound, a sulfone compound or a sulfonic ester compound is preferredbecause it is more stable against annealing at 160 or more and plasmathan a diazomethane compound.

[0095] Furthermore, an onium salt compound has a stronger property forinhibiting dissolution of a base polymer including a polyhydroxystyrenederivative than the other acid generators. Therefore, when the acidgenerator includes an onium salt compound, the solubility of theunexposed portion of the photosensitive material film 12 in thedeveloper can be reduced. Accordingly, the acid generator including anonium salt compound alone is good because the etching rate of thephotosensitive material film 12 in the plasma etching can be lowered.

[0096] Any onium salt compound may be used as far as it can generate anacid through irradiation with ArF excimer laser. Examples of the oniumsalt compound are a sulfonium salt compound such as triphenylsulfoniummethane, an iodonium salt compound such as diphenyliodoniumtrifluoromethane sulfonate, a pyridinium salt compound, a phosonium saltcompound, an oxonium salt compound and an ammonium salt compound.

[0097] Among the onium salt compounds, a sulfonium salt compound and aniodonium salt compound are particularly preferred, and preferableexamples of the sulfonium salt compound and the iodonium salt compoundare triphenylsulfonium triflate, triphenylsulfonium propionate,triphenylsulfonium hexaflate and diphenyliodonium triflate.

[0098] Now, the weight average molecular weight of the base polymer andthe mixing rate of the acid generator in the chemically amplified resistmaterial used in Embodiment 1 or 2 will be described.

[0099] The weight average molecular weight of the base polymer ispreferably 3000 through 30000 measured based on the gel permeationchromatography. When the weight average molecular weight is smaller than3000, the coating property of the photosensitive material film isdegraded, and when the weight average molecular weight exceeds 30000,the solubility in the developer is degraded so as to degrade the fineprocessing property. In contrast, when the weight average molecularweight is 3000 through 30000, the shape of the hole is not affected.

[0100] The mixing rate of the acid generator is preferably 0.1 through20 parts by weight based on 100 parts by weight of the polymer componentof the base polymer. When the mixing rate of the acid generator issmaller than 0.1 part by weight, the amount of the generated acid is toosmall to form a pattern, and when the mixing rate of the acid generatorexceeds 20 parts by weight, the whole acid generator cannot be dissolvedin the solvent. In contrast, when the mixing rate of the acid generatoris 0.1 through 20 parts by weight, the shape of the hole is notaffected.

[0101] EMBODIMENT 3

[0102] A method for forming a hole pattern according to Embodiment 3 ofthe invention will now be described with reference to FIGS. 3A through3C and 4A through 4C. FIG. 3B is a cross-sectional view taken along lineIIIB-IIIB of FIG. 3A, and FIG. 4C is a cross-sectional view taken alongline IVC-IVC of FIG. 4B.

[0103] A chemically amplified resist material used in Embodiment 3 isthe same as that of Embodiment 1 or 2.

[0104] First, as shown in FIGS. 3A and 3B, an anti-reflection film 22 isdeposited on an etch target film 21 of, for example, a BPSG film with athickness of 1200 nm deposited on a semiconductor substrate 20, and thechemically amplified resist material is applied on the anti-reflectionfilm 22. Thereafter, annealing is carried out at 90 for 90 seconds,thereby forming a photosensitive material film 23 with a thickness of700 nm. The anti-reflection film 22 is formed in order to suppress thestanding wave effect of the photosensitive material film 23 and toimprove the dimensional evenness.

[0105] Next, the photosensitive material film 23 is irradiated with ArFexcimer laser through a photomask having a transmission portion with adiameter of, for example, 200 nm, and annealing is then carried at 110for 90 seconds as the PEB. Subsequently, an irradiated portion (exposedportion) of the photosensitive material film 23 is dissolved in adeveloper of a 2.38% TMAH aqueous solution. Thus, the photosensitivematerial film 23 is formed into a hole pattern made from an unirradiatedportion (unexposed portion) of the photosensitive material film andhaving a hole 23 a with a hole size of 200 nm.

[0106] Then, as shown in FIG. 3C, the anti-reflection film 22 is etchedby using the hole-patterned photosensitive material film 23 as anetching mask, thereby forming a hole 22 a in the anti-reflection film22.

[0107] Next, as shown in FIG. 4A, the etch target film 21 is subjectedto plasma etching under the same conditions as in Embodiment 1 or 2 byusing the hole-patterned photosensitive material film 23 as an etchingmask. Thus, a hole 21 a is formed in the etch target film 21.

[0108] When the hole 21 a is thus formed in the etch target film 21, thehole 21 a can be formed in a circular plane shape with a hole size notlargely enlarged as compared with the desired value as shown in FIGS. 4Band 4C.

What is claimed is:
 1. A method for forming a hole pattern comprisingthe steps of: forming a photosensitive material film by applying, on anetch target film deposited on a semiconductor substrate, aphotosensitive material containing a hardly alkaline-soluble basepolymer including a polymer in which a principal chain has cycloolefinand a saturated or non-saturated polycyclic alkyl group is bonded to theprincipal chain, and an acid generator including an onium salt compound;forming a hole-patterned photosensitive material film by irradiatingsaid photosensitive material film with ArF excimer laser through aphotomask; and forming a hole pattern in said etch target film bysubjecting said etch target film to plasma etching using plasma at aplasma density of 1×10¹⁰/cm³ or more with said hole-patternedphotosensitive material film used as an etching mask.
 2. The method forforming a hole pattern of claim 1, wherein said polymer includes anorbornene derivative.
 3. The method for forming a hole pattern of claim1, wherein said polymer includes norbornene and a norbornene derivative.4. The method for forming a hole pattern of claim 1, wherein saidpolycyclic alkyl group is an adamantyl group, a tricyclodecyl group or atetracyclododecyl group.
 5. The method for forming a hole pattern ofclaim 1, wherein said plasma etching is carried out by using a firstvoltage for generating plasma and a second voltage for inducing ions ofthe plasma toward said semiconductor substrate.
 6. A method for forminga hole pattern comprising the steps of: forming a photosensitivematerial film by applying, on an etch target film deposited on asemiconductor substrate, a photosensitive material containing a hardlyalkaline-soluble base polymer including a polymer in which a principalchain is composed of cyclo with three or more folds ring, and an acidgenerator including an onium salt; forming a hole-patternedphotosensitive material film by irradiating said photosensitive materialfilm with ArF excimer laser through a photomask; and forming a holepattern in said etch target film by subjecting said etch target film toplasma etching using plasma at a plasma density of 1×10¹⁰/cm³ or morewith said hole-patterned photosensitive material film used as an etchingmask.
 7. The method for forming a hole pattern of claim 6, wherein saidpolymer includes a tricyclodecene derivative, a tetracyclododecenederivative, a pentacyclopentadecene derivative or a hexacycloheptadecenederivative.
 8. The method for forming a hole pattern of claim 6, whereina saturated or non-saturated polycyclic alkyl group is bonded to theprincipal chain of said polymer.
 9. The method for forming a holepattern of claim 6, wherein said plasma etching is carried out by usinga first voltage for generating plasma and a second voltage for inducingions of the plasma toward said semiconductor substrate.